[LEAD]We reported about the memorial service for the Korean victims of Japan's forced labor in the Sado Mines yesterday. Controversy is brewing as the bereaved families had to hold a separate event, as Japan refused to accept South Korea's request regarding the details of the memorial. Experts say that change in the government's Japan diplomacy is now inevitable. [REPORT]Japan promised to install exhibits on forced labor of Koreans and hold a memorial service for them every year if Korea agreed to the Sado mines' designation as a UNESCO World Heritage site.There were widespread concerns that Japan would fail to deliver, as it did after the Hashima Island inscription in 2015.But Seoul agreed to the addition of the Sado mines on the UNESCO list, saying that Tokyo showed sincerity and acknowledged the forceful use of Korean laborers.Cho Tae-yul/ Minister of Foreign affairs (Aug., Nat'l Assembly)You're criticizing me for abandoning the expression 'forced', But I didn't.However, the word "forced" is nowhere to be found at the Japanese exhibits put on display around the mines. The expression was also missing in the memorial speech.In response to the Korean government's request to send a vice minister-level official to the memorial ceremony, Tokyo sent Akiko Ikuina, parliamentary vice minister of Japan's Foreign Ministry and a far-right politician who has visited the controversial Yasukuni Shrine.Having failed to persuade Japan, the government decided to boycott the ceremony the day before it was held. But it did not express regret or issue an official protest. The bereaved families of the Korean forced laborers who had already traveled to Japan to attend the Japan-hosted event had to hold a separate memorial ceremony.Prof. Lee Won-deok/ Kookmin Univ.The fact that far-right figure attended the memorial runs counter to the agreement's purpose. Our officials are also at fault for falling short of it.If Japan continues to hold the memorial this way, it will be more difficult for the government to avoid criticism for its diplomatic blunder. Accordingly, Seoul is deliberating on follow-up responses.However, Japan is now shifting responsibility to Korea and it's uncertain if it will change its attitude.As Tokyo laid blame on Seoul, the government refuted that a key factor in its boycott decision was the fact that Japan's memorial speech and other details regarding the ceremony fell short of the agreement the two countries reached before the UNESCO designation of the Sado mines.The government will reportedly consider lodging a complaint about Japan's breach of promise with UNESCO.There are predictions that the government, which has stressed improving ties and made series of concessions to Tokyo, will inevitably have to revise its diplomacy towards Japan.